U.S. patent number 6,627,025 [Application Number 09/647,236] was granted by the patent office on 2003-09-30 for method and apparatus for extruding easily-splittable plural-component fibers for woven and nonwoven fabrics.
This patent grant is currently assigned to Hills, Inc.. Invention is credited to Jing-Peir Yu.
United States Patent |
6,627,025 |
Yu |
September 30, 2003 |
Method and apparatus for extruding easily-splittable
plural-component fibers for woven and nonwoven fabrics
Abstract
A spinneret 20 for producing easily splittable plural-component
fibers includes two passages 22 and 26 for respectively delivering
two incompatible polymers (A and B) to two sets of inclined
capillaries 34-39, 46-51. The two sets of capillaries converge
toward each other in a downstream direction and direct molten
polymer streams to two respective rows of orifices 40-45, 52-57.
The centerlines of the polymer A capillaries lie along axes that,
when extended beyond the spinneret, are offset and non-intersecting
with axes along which the centerlines of the polymer B capillaries
lie, such that the centerlines of the extruded polymer streams are
directed along non-intersecting axes. The capillary angles and
orifice arrangement cause the extruded polymer streams to extend
toward each other in an interleaved fashion, with the polymer
streams contacting each other in a generally tangential manner.
Inventors: |
Yu; Jing-Peir (late of
Pensacola, FL) |
Assignee: |
Hills, Inc. (West Melbourne,
FL)
|
Family
ID: |
22149820 |
Appl.
No.: |
09/647,236 |
Filed: |
December 21, 2001 |
PCT
Filed: |
March 25, 1999 |
PCT No.: |
PCT/US99/06517 |
PCT
Pub. No.: |
WO99/48668 |
PCT
Pub. Date: |
September 30, 1999 |
Current U.S.
Class: |
156/167; 156/181;
264/172.14; 425/131.5; 425/463; 425/72.2 |
Current CPC
Class: |
B29C
48/05 (20190201); B29C 48/19 (20190201); D01D
5/32 (20130101); B29C 48/345 (20190201); B29C
48/2888 (20190201); B29K 2023/12 (20130101); B29K
2105/0845 (20130101); B29C 48/29 (20190201); B29K
2067/00 (20130101); B29C 48/297 (20190201); B29K
2105/0809 (20130101); B29C 48/08 (20190201) |
Current International
Class: |
D01D
5/32 (20060101); D01D 5/30 (20060101); B29C
47/04 (20060101); B29C 47/10 (20060101); B29C
47/30 (20060101); B29C 047/30 (); D01F
008/04 () |
Field of
Search: |
;156/180,181,167
;425/72.2,131.5,463 ;264/172.14 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yao; Sam Chuan
Attorney, Agent or Firm: Edell, Shapiro & Finnan LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from U.S. Provisional Patent
Application Serial No. 60/079,323, entitled "Easily Splittable
Multi-segment Ribbon Shaped Conjugate Fibers for Non-woven
Fabrics," filed Mar. 25, 1998. The disclosure of this provisional
patent application is incorporated herein by reference in its
entirety.
Claims
What is claimed is:
1. A method of forming an easily splittable plural-component fiber
from plural extruded materials, the method comprising the steps of:
(a) directing a plurality of first streams of a first material to
respectively flow through a plurality of first capillaries to a
plurality of first orifices; (b) directing a plurality of second
streams of a second material to respectively flow through a
plurality of second capillaries to a plurality of second orifices
that are separate from the first orifices; (c) extruding the first
streams from the first orifices such that, at the first orifices,
the centerlines of the first streams are directed along respective
first axes; and (d) extruding the second streams from the second
orifices such that, at the second orifices, the centerlines of the
second streams are directed along second axes that are interleaved,
angled and non-intersecting with respect to the first axes such
that surfaces of the first streams contact and adhere to surfaces
of the second streams to form a plural-component fiber having a
transverse cross-section of interleaved segments of the first and
second materials.
2. The method of claim 1, wherein the extruded first and second
streams form a plural-component fiber having a substantially
ribbon-shaped transverse cross-section.
3. The method of claim 2, wherein the extruded first and second
materials form a ribbon-shaped plural-component fiber having a
ripple-shaped surface.
4. The method of claim 1, wherein the extruded first and second
streams form a plural-component fiber having an elongated, curved
transverse cross-sectional shape.
5. The method of claim 1, wherein: step (c) includes extruding each
of the first streams with a transverse cross-sectional shape that
is one of: substantially circular, substantially triangular,
substantially square or diamond-shape, and substantially
multi-lobal; and step (d) includes extruding each of the second
streams with a transverse cross-sectional shape that is one of:
substantially circular, substantially triangular, substantially
square or diamond-shape, and substantially multi-lobal.
6. The method of claim 1, wherein the plural-component fiber formed
by steps (a) through (d) is a bicomponent fiber.
7. The method of claim 1, wherein the first and second streams are
extruded at substantially the same speed.
8. The method of claim 1, wherein steps (a) and (b) include
directing the first and second streams to respectively flow through
the first and second capillaries with a spinneret.
9. A method of forming an easily splittable plural-component fiber
from plural extruded materials, the method comprising the steps of:
(a) directing a first stream of a first material to flow through a
first capillary to a first orifice; (b) directing a second stream
of a second material to flow through a second capillary to a second
orifice that is separate from the first orifice; (c) directing a
third stream of a third material to flow through a third capillary
to a third orifice that is separate from the first and second
orifices; (d) extruding the first stream from the first orifice
such that, at the first orifice, the centerline of the first stream
is directed along a first axis; (e) extruding the second stream
from the second orifice such that, at the second orifice, the
centerline of the second stream is directed along a second axis
that is non-intersecting with the first axis, the second axis being
angled with respect to the first axis and the first and second
orifices being relatively positioned such that a surface of the
extruded first stream contacts and adheres to a surface of the
extruded second stream to form the plural-component fiber; and (f)
extruding the third stream from the third orifice such that, at the
third orifice, the centerline of the third stream is directed along
a third axis that is non-intersecting with the first and second
axes, the third axis being angled with respect to the first and
second axes and the first, second and third orifices being
relatively positioned such that a surface of the extruded third
stream contacts and adheres to a surface of the extruded second
stream to form a multi-component fiber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for
producing plural-component filament or fiber yarns having
individual constituent micro-denier sub-filaments or sub-fibers
that are easily separated and, in particular, to a method and
apparatus for extruding easily splittable plural-component fibers
suitable for making nonwoven fabrics in a spunbond process or woven
fabrics.
2. Description of the Related Art
Various attempts have been made to produce woven and nonwoven
fabrics having improved characteristics, such as greater bulkiness
and softness, superior flexibility and drape, and better barrier
and filtration properties for use in products such as disposable
absorbent articles, medical garments and filtration materials. It
has been found that nonwoven fabrics having desirable qualities can
be manufactured from splittable plural-component fibers. Such
plural-component fibers typically include at least two different
polymers arranged as microfilaments or segments across the
transverse cross section of the fiber, which segments extend
continuously along the length of the fiber. By separating these
plural-component fibers into their constituent segments after
extrusion, a fine denier fabric with desirable characteristics can
be produced.
Such a finer denier fabric is difficult to produce without
employing splittable plural-component fibers. Individual fibers
having a transverse cross-sectional area comparable to a single
segment of a plural-component fiber are difficult to manipulate and
generally cannot withstand the drawing process applied to attenuate
extruded fibers without breakage. The use of plural-component
fibers permits formation of a finer denier fabric, because plural
fiber segments are joined to each other during at least a portion
of the drawing and attenuation process, thereby forming a thicker
combined fiber that can more readily be drawn and attenuated. Once
drawn, the plural-component fibers can then be split into very fine
sub-fiber segments.
A known method of producing plural-component fibers includes
side-by-side merging of a plurality of sub-streams of polymers into
a combined conjugated stream in a counterbore of a spinneret. As
shown in FIG. 1, sub-streams of two incompatible polymers (polymers
A and B) are introduced into the counterbore 12 of a spinneret 10
and brought into contact with each other. As used herein in the
context of polymers, the term "incompatible" refers to different
polymers that do not strongly bond or strongly adhere to each
other, but that will cling or somewhat adhere to each other when
adjacently extruded in a molten state from a spinneret and, when
arranged side-by-side, can later be separated from each other with
a limited degree of effort. The adjacent polymer sub-streams form a
combined stream that flows through the orifice 13 of the spinneret,
and the stream is then quenched to form a spun plural-component
fiber.
The most common synthetic textile fibers used in fabrics are made
from polymer materials such as nylon (e.g., nylon 66, nylon 6),
polyester, polyolefin, and their copolymers. All of these polymers
are melt spinnable. Some nonwoven fabrics made from carded or
air-laid webs comprise rayon or acrylic fibers.
Many of the nonwoven fabrics made from melt-spinnable polymers are
produced using a spunbond process. The term "spunbond" refers to a
process of forming a nonwoven fabric or web from thin fibers or
filaments produced by extruding molten polymers from orifices of a
spinneret. More specifically, as shown in FIG. 2, a plurality of
plural-component fibers is extruded through orifices of a spinneret
to form a vertically oriented curtain of downwardly moving fibers.
The fibers are quenched and then enter an air aspirator 14
positioned below the spinneret, which aspirator introduces a
rapidly downward moving air stream produced by compressed air from
one or more air aspirating jets. The air stream creates a drawing
force on the fibers, causing them to be drawn between the spinneret
and the air jet, thereby longitudinally stretching and transversely
attenuating the fibers. The drawn fibers exit at the bottom of the
jet or jets and are randomly laid on a forming surface 16, such as
a moving conveyor belt, to form a continuous nonwoven web of
fibers. The web is subsequently bonded using one of several known
techniques to form the nonwoven fabric, e.g., by being pressed
between a pair of hot calender rolls. Carded or air-laid webs can
also be formed from these polymers.
In the case of woven fabrics, the extruded fibers are typically
quenched and drawn prior to being wound on a bobbin. Thereafter, in
a separate process, a conventional knitting or weaving technique is
employed to form a woven fabric from the fibers.
A number of known techniques can be used to separate the individual
segments of plural-component fibers prior or subsequent to
formation of the fabric. Specifically, fiber segments can be
separated by applying mechanical force to the fibers, such as high
pressure water or air jets or air turbulence, beating, carding,
calendering, or other mechanical working of the fibers. In the case
of woven fabrics, the fabric can be brushed or sanded to abroad and
separate fibers. Another process for separating segments of
plural-component fibers involves applying a hot aqueous solution to
the fibers to induce splitting or treating the fibers with
chemicals. Specifically, the fibers may be transported through a
hot water bath or sprayed with steam or a mixture of steam and air.
Other techniques have also been proposed, such as developing a
triboelectric charge in at least one of the components and/or
applying an external electric field to the fibers. Alternatively,
one of the components of the plural-component fibers can be
dissolved by a solvent applied to the fiber, such that segments
formed of the undissolved component remain.
The required treatment of the fibers in the fabric adds cost to the
process and introduces the possibility of damage to the fabric. If
chemical treatment is involved, loss of polymer results in certain
cases, and the additional problem of recycling, disposal and
handling of the chemicals exists. Moreover, limited or incomplete
fiber splitting may result, depending on the particular polymers,
the extrusion process, and the splitting technique applied. In
particular, the extent of fiber splitting may be limited at higher
spinning and web formation belt speeds, thereby constraining the
rate at which the nonwoven fabric can be produced. These problems
can be mitigated by forming plural-component fibers that are easily
splittable.
It has been found by the present inventor that easier splitting of
a bicomponent fiber comprising two adjacent segments formed of
incompatible polymers can be achieved by keeping the polymer
sub-streams separated from each other in the spinneret and merging
the side-by-side sub-streams into a combined stream just below the
face of spinneret from which the sub-streams are extruded via two
separate orifices. As described in U.S. Pat. No. 5,093,061 (the
'061 patent), the disclosure of which is incorporated herein by
reference in its entirety, by combining the sub-streams only after
the sub-streams have been extruded, the adhesion between the
sub-fibers is sufficiently light that the fiber splits
substantially completely into the sub-fiber segments upon
application of boiling water.
While the aforementioned patent discloses the technique of
combining two streams below the spinneret to form an easily
splittable bicomponent fiber, the process described therein has a
number of limitations. Specifically, the process is limited to an
arrangement wherein two sub-streams are aimed directly toward each
other (i.e., the sub-streams are directed along axes that
intersect, the axes being co-planar in a vertical plane), such that
substantial surface areas of the sub-streams come into contact with
each other at the point of sub-stream intersection to produce a
side-by-side two-segment fiber.
The geometry (i.e., co-planar intersecting axes) of that system is
not readily extendable to production of multi-component fibers. In
particular, the technique disclosed in the '061 patent cannot be
used to generate plural-component fibers having an elongated or
ribbon-shaped transverse cross-section with three or more
sub-fibers or segments, since the polymer streams merge at a common
point. Further, while the degree of sub-fiber adherence is reduced
by joining the polymer sub-streams below the spinneret, the
centerline intersection of the sub-streams causes the sub-fibers to
contact and adhere to each other over a substantial portion of
their surface areas, thereby forming a significant bond.
Moreover, the system disclosed in the '061 patent involves winding
the two-segment fiber onto a package immediately after quenching of
the fiber without splitting the fiber. The unsplit fiber is
subsequently woven or knitted, and split only when the resulting
woven fabric is subjected to boiling water in a scouring and dying
process. It is desirable that the sub-fibers of the two-segment
fibers be sufficiently bonded to each other to avoid separation
during the winding, handling and weaving processes that occur prior
to the dying process. Thus, the '061 patent does not suggest fiber
splitting in the context of spunbond or nonwoven fabric formation,
where splitting in line with fiber extrusion is desirable.
Acordingly, there remains a need for a system capable of producing
easily splittable plural-component fiber useful for in-line fiber
splitting in a simple, inexpensive and rapid spunbond process to
form nonwoven fabrics having a fine denier and good fabric
characteristics.
SUMMARY OF THE INVENTION
It is an object of the present invention to produce
plural-component synthetic fibers whose constituent sub-fibers or
segments are easily separated from each other, which fibers are
useful for forming woven and nonwoven fabrics.
It is another object of the present invention to minimize the
contact surface area between adjacent segments of a
plural-component fiber to improve the separability of the
segments.
It is another object of the present invention to produce
plural-component fibers having a high aspect ratio, such as
ribbon-shaped fibers, to improve process efficiency and fabric
quality.
It is a further object of the present invention to achieve a high
degree of separation between segments of plural-component fibers in
an in-line spunbond process to produce a nonwoven fabric having a
fine denier.
It is a still further object of the present invention to rapidly
separate constituent fiber segments of plural-component fibers in
an in-line spunbond process using a relatively simple, reliable and
inexpensive mechanism.
It is another object of the present invention to produce a nonwoven
fabric having superior properties, such as good coverage (i.e., no
openings or gaps), bulkiness, softness, flexibility and drape, and
good barrier properties.
It is yet another object of the present invention to form a fiber
web that can more readily be bonded to form nonwoven fabric.
The aforesaid objects are achieved individually and in combination,
and it is not intended that the present invention be construed as
requiring two or more of the objects to be combined unless
expressly required by the claims attached hereto.
According to the present invention, easily splittable
plural-component synthetic fibers are formed by separately
extruding individual molten polymer streams from orifices of a
spinneret and joining the extruded polymer streams below the
downstream face of the spinneret. The polymer streams are merged
into a combined polymer stream by extruding the polymer streams in
directions that cause surfaces of the streams to contact each other
and adhere. The relative position of the orifices from which the
polymer streams are extruded, the number of orifices, and the
direction of extrusion of the individual streams determine the
overall transverse cross-sectional shape of the resulting
plural-component fiber. The centerlines of the extruded polymer
streams are offset (i.e., non-intersecting) with each other, such
that surfaces of adjacent streams contact each other in a somewhat
tangential or glancing manner, thereby minimizing the surface area
of each polymer stream that adheres to adjacent streams to
facilitate subsequent easy separation of the fiber segments formed
by the quenched streams.
According to an exemplary embodiment, a spinneret for producing
easily splittable plural-component fibers includes two separate
slot-shaped passages for respectively delivering two incompatible
polymers (polymers A and B) to two sets of inclined capillaries.
The two sets of capillaries converge toward each other in a
downstream direction and direct molten polymer streams to two
respective rows of orifices. The centerlines of polymer A
capillaries lie along axes that, when extended beyond the
spinneret, are offset and non-intersecting with axes along which
the centerlines of the polymer B capillaries lie. Accordingly, in
the direction of the rows of the orifices, the centers of the
polymer A orifices are offset with respect to the centers of the
polymer B orifices.
Polymers A and B are simultaneously extruded from their respective
orifices at substantially the same speed in directions dictated by
the angle and orientation of their respective capillaries.
Consequently, the centerlines of the extruded polymer A streams are
directed along axes that are non-intersecting with the axes along
which the centerlines of the extruded polymer B streams are
directed. The inclined angle of the capillaries and the arrangement
of the orifices cause the extruded streams of polymers A and B to
extend toward each other along offset centerline axes with the
polymer A streams being directed between the polymer B streams in
an interleaved fashion. The spacing between the orifices is set
such that the polymer A and B streams contact each other in a
generally tangential, glancing or grazing manner. More
specifically, to ensure that the interleaved extruded streams of
polymers A and B contact and adhere to each other to merge into a
combined stream below the face of the spinneret, the distance b
between the centerlines of adjacent same-polymer orifices is less
than the sum of the polymer A orifice diameter and the polymer B
orifice diameter.
The interleaved polymer streams contact each other to form a
combined stream. The combined stream then proceeds substantially
vertically downward and is subjected to a quenching process. By
joining the polymer streams below the spinneret, adjacent segments
of the resulting plural-component fiber are less strongly bonded to
each other than they would otherwise be if joined within the
spinneret and extruded from a single orifice. The offset
arrangement of the orifices reduces the strength of the bond
between adjacent fiber segments by limiting the surface area over
which the segments are in contact with each other in the resulting
plural-component fiber. The bond formed between adjacent segments
of the plural-component fibers is sufficiently strong to withstand
attenuation of the fibers without substantial separation, but
sufficiently weak to allow separation with only a modest amount of
separation processing.
Once quenched, the easily splittable plural-component fibers can be
used to form a woven or non-woven fabric using any of a variety of
fabric forming technologies. Likewise, the plural-component fibers
can be separated using any one or a combination of known
fiber-splitting techniques, including: mechanical working with high
pressure water or air jets or air turbulence, beating, carding,
calendering, and application of a hot aqueous solution, hot air
and/or steam. In accordance with one embodiment of the present
invention, in-line splitting of the plural-component fibers is
accomplished using differential heat shrinkage in a spunbond
process for forming nonwoven fabric.
The present invention is not limited to use of easily splittable
plural-component fibers in nonwoven fabrics formed from spunbond
process and encompasses processes for forming fabric from
plural-component fibers that do not require bonding of the fibers
(e.g., spun-laid or air carding processes). Further, the present
invention can be applied in melt blown systems. The benefits of
using easily splittable plural-component fibers are not limited to
systems that form webs from fiber filaments (i.e., continuous
fibers), and the present invention encompasses processes for
forming woven and nonwoven fabrics from split or splittable staple
fibers.
Further, formation of easily splittable plural-component fibers in
accordance with the present invention can be performed in
conjunction with other extrusion and fabric or material formation
techniques. For example, both splittable and non-splittable fibers
can be extruded from a single spinneret or plural spinnerets to
create a web having a mixture of different types of fiber or fiber
shapes. Further, a web formed from separated sub-fibers can be
coupled to (e.g., bonded to) other types of webs or laminates in,
for example, a multi-layered product.
The nonwoven fabric formed by the process of the present invention
is useful in any product where properties such as softness,
strength, filtration or fluid barrier properties, and high coverage
at a low fabric weight are desirable or advantageous, including,
but not limited to: disposable absorbent articles; medical barrier
fabrics; filtration media; and clothing liners.
The above and still further objects, features and advantages of the
present invention will become apparent upon consideration of the
following detailed description of a specific embodiment thereof,
particularly when taken in conjunction with the accompanying
drawings wherein like reference numerals in the various figures are
utilized to designate like components.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional side view in elevation of a
conventional spinneret for producing a side-by-side bicomponent
fiber.
FIG. 2 is a diagrammatic view of an apparatus for performing a
conventional spunbond process for forming nonwoven fabric from a
plurality of melt spun plural-component fibers.
FIG. 3 is a cross-sectional side view in elevation taken along
lines 3--3 of FIG. 4 of a spinneret for producing a ribbon-shaped
fiber in accordance with a preferred embodiment of the present
invention.
FIG. 4 is a cross-sectional top plan view taken along lines 4--4 of
FIG. 3 of the spinneret shown in FIG. 3.
FIG. 5 is a bottom plan view of the spinneret shown in FIG. 3.
FIG. 6 is a transverse cross-sectional view of an extruded
plural-component fiber of the present invention having a
ribbon-shaped transverse cross-section produced with a spinneret of
the type shown in FIGS. 3-5.
FIG. 7 is a transverse cross-sectional view of another extruded
plural-component fiber of the present invention having a
ribbon-shaped transverse cross-section produced with a spinneret of
the type shown in FIGS. 3-5, wherein the extruded polymer stream
merge at a greater distance from the spinneret.
FIG. 8 is a transverse cross-sectional view of a further extruded
plural-component fiber of the present invention having a
ribbon-shaped transverse cross-section, wherein individual fiber
segments have a generally triangular transverse cross-sectional
shape.
FIG. 9 is a transverse cross-sectional view of still another
extruded plural-component fiber of the present invention having a
ribbon-shaped transverse cross-section, wherein individual fiber
segments have a generally square or diamond-shaped transverse
cross-sectional shape.
FIG. 10 is a bottom plan view of a spinneret face having an orifice
with facing saw-tooth edges for forming a ribbon-shaped
plural-component fiber having segments with substantially
diamond-shaped transverse cross sections in accordance with one
embodiment of the present invention.
FIG. 11 is a bottom plan view of a spinneret face having an orifice
with facing concave arcuate edges for forming a ribbon-shaped
plural-component fiber having segments with rounded transverse
cross sections in accordance with another embodiment of the present
invention.
FIG. 12 is a bottom plan view of a spinneret face having an orifice
with facing convex arcuate edges for forming a ribbon-shaped
plural-component fiber having multi-lobal segments in accordance
with yet another embodiment of the present invention.
FIG. 13 is a bottom plan view of a spinneret face having an orifice
with facing undulating edges for forming a ribbon-shaped
plural-component fiber having segments with substantially
triangular-shaped transverse cross sections in accordance with
still another embodiment of the present invention.
FIG. 14 is a transverse cross-sectional view of yet another
extruded plural-component fiber of the present invention having a
C-shaped transverse cross-section.
FIG. 15 is a transverse cross-sectional view of an extruded
plural-component fiber of the present invention having an S-shaped
transverse cross-section.
FIG. 16 is a diagrammatic view of an apparatus for performing a
spunbond process employing fiber splitting in line with fiber
extrusion to form a nonwoven fabric.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, easily splittable
plural-component synthetic fibers are formed by separately
extruding individual molten polymer streams from orifices of a
spinneret and joining the extruded streams external to the
spinneret to form combined streams that are quenched to produce
plural-component fibers. Merging of the polymer streams into a
combined stream is achieved by extruding the polymer streams in
directions that cause surfaces of the streams to contact each other
and adhere. The relative positions of the orifices from which the
fiber streams are extruded, the number of orifices, and the
direction of extrusion of the individual streams determine the
overall transverse cross-sectional shape of the resulting
plural-component fiber. Upon quenching, the combined stream forms a
plural-component fiber, with the individual polymer streams forming
the separable segments of the plural-component fiber. Preferably,
the centerlines of the extruded fiber streams are offset (i.e.,
non-intersecting) from each other, such that surfaces of adjacent
streams contact each other in a somewhat tangential manner, thereby
allowing a wide variety of transverse cross-sectional shapes to be
produced, and minimizing the surface area of each stream that
adheres to adjacent streams to facilitate easy separation of the
fiber segments during subsequent processing.
As used herein, the terms "segment" and "sub-fiber" refer to a
portion of a fiber having a composition that is distinct from the
composition of another portion of the fiber, and the term
"bicomponent" refers to a fiber having two or more segments,
wherein at least one of the segments comprises one material or
component (e.g., a polymer), and the remaining segments comprise
another, different material or component. The term
"plural-component", as used herein, refers to a fiber having two or
more segments, wherein each segment comprises one of at least two
different materials or components which make up the fiber (thus, a
bicomponent fiber is a type of plural-component fiber).
An exemplary embodiment of a spinneret 20 useful for producing
easily splittable plural-component fibers in accordance with the
present invention is illustrated in FIGS. 3-5. The spinneret
includes a first counterbore or slot-shaped passage 22 having an
upstream opening 24 for receiving a stream of a molten polymer A,
and a second counterbore or slot-shaped passage 26 having an
upstream opening 28 for receiving a stream of a molten polymer B.
Polymers A and B are preferably incompatible polymers that will
adhere to each other in a molten or semi-molten state, and remain
weakly bonded upon quenching, but that do not strongly bond or tend
to readily intermix. For example, polymers A and B can comprise any
combination of melt spinnable resins, including, but not limited
to: homopolymer and copolymers of polypropylene, polyethylene
(e.g., polyethylene terephthalate), polyester, polyactic acid,
nylon and poly(trimethylene terephthalate).
As best seen in FIG. 3, counterbores 22 and 26 extend side-by-side
generally vertically from upstream openings 24 and 28 to downstream
or bottom end surfaces 30 and 32, respectively, and maintain
separate flow paths for polymers A and B. Counterbores 22 and 26
have an elongated or generally slot-shaped cross-section transverse
to the direction of polymer flow, with the longer transverse sides
of counterbores 22 and 26 extending side-by-side within spinneret
20 (see FIG. 4).
A row of inclined, substantially cylindrical capillaries 34-39
extend from the downstream surface of counterbore 22 to a row of
respective circular orifices 40-45 in a downstream (bottom) surface
33 of spinneret 10. More specifically, a row of six circular holes
in the downstream surface 30 of counterbore 22 define upstream
openings of capillaries 34-39 and extend in a line parallel to the
longer transverse side of counterbore 22. A parallel row of six
circular holes formed in downstream surface 32 of counterbore 24
respectively define upstream openings of another row of inclined,
substantially cylindrical capillaries 46-51 which extend from
counterbore 24 to a row of respective circular orifices 52-57 in
the downstream face of spinneret 20.
The centerlines of capillaries 34-39 are substantially parallel to
each other, and the centerlines of capillaries 46-51 are
substantially parallel to each other. Capillaries 34-39 and
capillaries 46-51 are inclined in a downstream direction toward a
vertical centerline lying between counterbores 22 and 24, such that
the distance between the two rows of capillaries decreases in a
downstream direction from the counterbores to the orifices. Stated
differently, the two rows of capillaries 34-39 and 46-51 converge
toward each other as they approach the downstream orifices. At
least in the vicinity of the orifices, the centerlines of
capillaries 34-39 lie along axes that, when extended beyond the
spinneret, are offset and non-intersecting with axes along which
the centerlines of capillaries 46-51 lie.
As best seen in FIG. 5, orifices 40-45 are positioned at regular
intervals along a first line, with centers of adjacent orifices
spaced apart by a distance b. Orifices 52-57 are positioned at
regular intervals along a second line that is parallel to the first
line, with centers of adjacent orifices spaced apart by distance b.
The first and second lines extending through the centers of the two
rows of orifices are spaced apart by a distance c. Each of orifices
40-45 has a diameter d1, and each of orifices 52-57 has a diameter
d2. In the direction of the first and second lines, the centers of
orifices 40-45 are offset with respect to the centers of orifices
52-57, such that each of orifices 41-45 is substantially centered
(in the direction of the lines) between adjacent pairs of orifices
52-57, and each of orifices 52-56 is substantially centered (in the
direction of the lines) between adjacent pairs of orifices
40-45.
As molten polymer streams A and B respectively flow to the
downstream surfaces 30 and 32 of counterbores 22 and 24, the
polymer streams simultaneously enter the two rows of capillaries
and flow downstream toward the two rows of orifices. Each of the
polymer streams is extruded from its respective orifice in a
direction dictated by the angle and orientation of the capillary.
Thus, at the point of extrusion from the orifice, each polymer
stream is directed substantially along the axis of the centerline
of its capillary. Consequently, the centerlines of the extruded
polymer A streams are directed along axes that are non-intersecting
with the axes along which the centerlines of the extruded polymer B
streams are directed. However, the centerline axes of the polymer A
streams lie in a plane that intersects a plane in which the
centerline axes of the polymer B streams lie, with the planes
intersecting along a substantially horizontal line below the
downstream face of the spinneret (hereinafter denoted as "the line
of convergence"). The inclined angle of the capillaries, the
distance c between the rows of orifices, and the relative positions
of the orifices are arranged such that the extruded streams of
polymers A and B extend toward each other along offset centerline
axes. That is, the polymer A streams extruded from orifices 30-35
are not aimed directly toward the polymer B streams extruded from
orifices 42-47; rather, the polymer A streams are directed between
the polymer B streams in an interleaved fashion.
The spacing between the orifices is set such that the polymer A and
B streams contact each other in a generally tangential manner. More
specifically, to ensure that the interleaved extruded streams of
polymers A and B contact and adhere to each other to merge into a
combined stream below the face of the spinneret, the distance b
between two adjacent polymer A orifices 40-45 (also the distance b
between two adjacent polymer B orifices 52-57) must be less than
the sum of the polymer A orifice diameter d1 and the polymer B
orifice diameter d2 (b<d1+d2). However, to minimize the amount
of surface area over which adjacent stream contact (and hence the
amount of surface area over which segments of the plural-component
fiber adhere), it is preferable that the distance b be as close as
possible to the sum of the diameters d1 and d2 while still
achieving consistent adherence of adjacent streams. As a result,
adjacent streams contact each other in a substantially grazing or
glancing manner.
The interleaved polymer streams contact each other substantially
along the horizontal line of convergence between the aforementioned
axial planes to form a combined stream. The combined stream then
proceeds substantially vertically downward and is subjected to a
quenching process. By joining the polymer streams below the
spinneret, adjacent segments of the resulting plural-component
fiber are less strongly bonded to each other than they would
otherwise be if joined within the spinneret and extruded from a
single orifice. This may be due in part to the fact that some
degree of cooling or quenching of the polymer streams occurs prior
to merging of the streams below the spinneret, with the semi-molten
streams having less tendency to bond to each other than molten
streams within the spinneret. Further, the individual polymer
streams have less surface energy when joined outside the spinneret
and are not compressed together as they would be if joined within
the spinneret, resulting in weaker inter-stream bonds. Another
factor reducing the strength of the bond between adjacent fiber
segments is the limited surface area over which the segments are in
contact with each other as a result of the offset arrangement of
the orifices. The bond formed between adjacent segments of the
plural-component fibers is sufficiently strong to withstand
attenuation of the fibers without substantial separation, but
sufficiently weak to allow separation with only a modest amount of
separation processing.
The angle of convergence between the extruded polymer A streams and
the extruded polymer B streams (i.e., angle formed between two sets
of capillaries) can be any angle that causes the streams to merge
at a short distance (e.g., no more than several millimeters) below
the lower face of the spinneret. For example, the angle of
convergence can be between approximately 20.degree. and 30.degree..
The distance c between the first line along the polymer A orifices
lie and the second line along which the polymer B orifices lie is
set in conjunction with the angle of convergence to control the
distance between the spinneret face and the line of convergence.
For example, the distance c can be on the order of the spacing b
between adjacent same-type polymer orifices. The orifice diameters
d1 and d2 are preferably less than approximately 0.3 mm in
diameter, more preferably less than approximately 0.2 mm diameter
and, for certain applications, preferably less than approximately
0.1 mm. It is to be understood that these dimensions are provided
by way of example only and are not in any way limiting on the scope
of the invention unless specifically required by the appended
claims.
To facilitate smooth formation of plural-component fibers, the
streams of molten polymer A are extruded at substantially the same
speed as the streams of molten polymer B. If necessary, the
diameter d1 of the polymer A orifices 40-45 may be different from
the diameter d2 of the polymer B orifices 52-57 to yield
substantially equal polymer extrusion speeds. Further, the
diameters d1 and d2 can be set to different values in accordance
with a desired volume ratio of polymers A and B in the resulting
plural-component fiber. For example, when the desired A:B volume
ratio is 1:1, diameter d1 is set equal to diameter d2. For circular
orifices, where the desired volume ratio is n:1, the diameter ratio
is set to n.sup.1/2 :1. More generally, for any shape of orifice,
when the desired A:B volume ratio of the plural-component fiber is
n:1, the ratio of the areas of the orifices is set to n:1.
The arrangement of the spinneret and orifices shown in FIGS. 3-5
produces a ribbon-shaped combined stream which, after being
quenched, forms a ribbon-shaped fiber having a substantially
straight or flat transverse cross-sectional shape with alternating
side-by-side segments of polymers A and B, as shown in FIG. 6. Each
segment adjoins adjacent segments along lines extending between the
longer edges of the ribbon. The fiber shown in FIG. 6 is formed
from streams that converge and merge into a single stream while the
polymer streams are still substantially molten, resulting in a
substantially smooth surface. If the streams merge at a greater
distance below the downstream face of the spinneret, the individual
streams have an opportunity to cool slightly prior to merging;
consequently, the segments of the resulting plural-component fibers
may retain the shape of the individual streams to a greater degree,
as shown in transverse cross-section in FIG. 7. As a result, the
plural component fiber is formed with a ripple-shaped surface,
wherein the segments adhere to each other along a reduced surface
area (relative to the fiber shown in FIG. 6) and are easier to
separate from each other during subsequent processing.
The formation of splittable ribbon-shaped plural-component fibers
provides a number of advantages over plural-component fiber having
other transverse cross-sectional shapes. More specifically,
ribbon-shaped fibers having an aspect ratio of at least 3.0
(defined as the ratio of the length to width of the transverse
cross-section of the fiber) have been found to provide unexpected
efficiencies in the fiber drawing process. As described in
International Patent Application No. PCT/US98/25627, the disclosure
of which is incorporated herein by reference in its entirety, an
aspirator is typically employed to draw the fibers after extrusion.
The aspirator uses air pressure to form an air flow directed
generally downward, which creates a downward air drag on the
fibers, thereby increasing the velocity of the portion of the
fibers in and below the aspirator relative to the velocity of the
portion of the fibers above the aspirator. The downward drawing of
the fibers longitudinally stretches and transversely attenuates the
fibers. The greater surface area (resulting from a larger
transverse perimeter and a high aspect ratio) of each ribbon-shaped
fiber allows the downwardly directed air in the aspiration unit to
"grip" the fiber better due to increased downward drag on the
fibers, hence achieving a fiber velocity closer to the aspirator's
downward air velocity. This increased fiber velocity results in
fibers of desirably lower denier at a given air pressure and air
consumption. Stated in another way, the increased downward drag
permits a lower air pressure and air consumption to produce
ribbon-shaped fibers having the same denier as low aspect fibers
drawn at higher air pressures, hence providing the potential to
reduce energy costs.
Moreover, where subsequent splitting of the fiber segments is
achieved using differential heat shrinkage of two different polymer
components, plural-component fibers having a ribbon-shaped
cross-section have been found to provide faster and more complete
segment separation relative to plural-component fibers having other
transverse cross sectional shapes. Further, when incomplete
splitting of the fibers occurs, the ribbon-shaped fiber still
results in a very soft fabric relative to other fiber
cross-sections, because of the shape of the ribbon produces a very
low bending modulus (i.e., the unseparated portions of the ribbon
fibers can still twist and bend in three dimensions, and the
adjoining separated portion of the fibers have a high degree of
freedom to bend in different directions relative to each other).
Thus, in accordance with the present invention, use of
plural-component fibers having a ribbon-shaped cross section with
segments of alternating components is desirable because: 1) they
split easily and almost totally; and 2) to the extend that the
fiber segments do not separate, the unsplit ribbon-shaped fiber is
by far softer than unsplit fibers of other transverse cross
sections.
To further reduce the surface area over which adjacent segments of
the plural-component fibers are joined, the cross-section of the
capillaries and orifices can be other than circular. For example,
the capillaries and orifices (and hence the extruded polymer
streams) can have substantially triangular transverse
cross-sectional shapes, such that the streams contact adjacent
streams at edges formed by the triangle points (albeit somewhat
rounded at the time of contact), as shown in FIG. 8. Similarly, the
orifices can have a square or diamond shape, such that adjacent
polymer streams join at the corners of the squares or diamonds, as
shown in FIG. 9. Polymers extruded with other regular or irregular
transverse cross-sections are suitable for use with the present
invention, including, but not limited to, polymer streams having
multi-lobal transverse cross sections (e.g., trilobal or
star-shaped). These orifice/polymer stream non-circular transverse
cross-sectional shapes produce fiber segments that are attached to
adjacent segments over a relatively small surface area, allowing
individual segments to freely pivot about their attachment points.
As a result, ribbon-shaped fibers formed of triangular,
diamond-shaped or multi-lobal segments have an even lower bending
modulus than comparable ribbon-shaped fibers formed of segments
having a circular transverse cross-sectional shape, and
consequently form even softer fabrics.
In accordance with another aspect of the present invention,
plural-component fibers having an elongated transverse cross
section and reduced surface area in contact between adjacent
segments can be extruded from a single, elongated orifice having
facing undulating edges. For example, a ribbon-shaped fiber having
diamond-shaped segments can be formed by extruding plural
side-by-side polymer streams of interleaved components from an
orifice having facing saw-tooth edges (FIG. 10), with each polymer
stream being extruded between tips of adjacent teeth. Other segment
shapes can be produced from orifices with other undulating shapes,
such as facing arcuate sections or facing U-shaped sections (see
FIGS. 11-13). In each case, adjacent polymer streams meet at
periodic points along the undulating pattern, preferably at points
where the orifice has a local minimum transverse width in order to
minimize the surface area over which the streams (and segments)
contact each other. As used herein, the term "local minimum
transverse width" refers to a transverse distance across the
orifice that is less than the transverse distance across the
orifice to either side. Thus, for example, the opposing pointed
tips of the teeth of the saw-tooth edges for a location where the
orifice has local minimum transverse width.
While the bonds formed between adjacent segments extruded from a
single orifice in this manner are stronger than those formed
between comparable segments formed by separate extrusion of the
polymer streams, the reduced surface area between adjacent segments
results in easier separation of segments and a lower bending
modulus (relative to a comparable flat ribbon-shaped
plural-component fiber).
While the exemplary embodiment shown in FIGS. 3-5 produces a
ribbon-shaped bicomponent fiber whose transverse cross-section is
elongated along a substantially straight line, it will be
understood that virtually any desired transverse cross-sectional
fiber shape can be achieved by controlling the number of orifices,
the relative positions of the orifices, and the angle of
convergence of each of the capillaries. For example, by suitably
arranging the layout pattern of the orifices, plural-component
fibers having curved ribbon-shaped transverse cross sections, such
as those shown in FIGS. 14 and 15, can be produced. In other words,
the "line of convergence" need not be a line, but can be a curve,
and the curve along which the polymer streams merge need not lie in
a horizontal plane or be parallel with the downstream face of the
spinneret.
Furthermore, in accordance with the present invention any number,
combination or arrangement of counterbores, polymer flow paths,
capillaries, and orifices can used to produce a plural-component
fiber, provided that at least some number of polymer streams are
extruded along non-intersecting centerlines and are joined external
to the spinneret to form a plural-component fiber. Thus, for
example, the capillaries which deliver the polymer streams to the
orifices need not be cylindrical, straight, parallel to
like-polymer capillaries or lie along a common plane. Further, the
polymer streams forming a single plural-component fiber need not
join at the same distance from the spinneret. For instance, two
streams may merge just below the spinneret, with a third stream
joining the two streams at a greater distance from the
spinneret.
While shown in the exemplary embodiment as producing a
ribbon-shaped plural-component fiber comprising several segments,
it will be understood that the principle of the present invention
can be applied using as few as two segments, where the centerlines
of the two extruded polymer streams lie along non-intersecting
axes, such that the two streams contact each other in a somewhat or
generally tangential, glancing or grazing manner after extrusion
and adhere to each to form a two-segment, bicomponent fiber.
Moreover, while the foregoing examples depict bicomponent fibers,
it will be understood that the present invention can be applied
using three (e.g., polymers A, B and C) or more different polymers
interleaved to form an easily splittable multi-component fiber.
The easily splittable plural-component fiber produced in accordance
with the present invention can be used in a spunbond process to
produce a non-woven fabric having desirable properties. For
example, the plural-component fiber extrusion technique of the
present invention can be used in conjunction with the in-line fiber
splitting spunbond system disclosed in International Patent
Application No. PCT/US98/21378, the disclosure of which is
incorporated herein by reference in its entirety. The term
"in-line", as used herein refers to a process wherein fiber
extrusion, splitting and web formation are performed in a single,
continuous process (i.e., not in-line would be if the extruded
fibers are made into a roll and then split or formed into a web
separately).
FIG. 16 diagrammatically illustrates an apparatus 100 for producing
a nonwoven fabric according to an in-line spunbond process.
Apparatus 100 includes hoppers 102 and 104 into which pellets of
two different polymers, polymers A and B, are respectively placed.
Polymers A and B are respectively fed from hoppers 102 and 104 to
screw extruders 106 and 108 which melt the polymers. The molten
polymers respectively flow through heated pipes 110 and 112 to
metering pumps 114 and 116, which in turn feed the two polymer
streams to a suitable spin pack 118. Spin pack 118 includes a
spinneret 120 with orifices 122 for producing easily splittable
plural-component fibers in the aforementioned manner. By way of
non-limiting example, orifices 122 may be arranged to extrude a
substantially horizontal, rectangular array of plural-component
fibers.
As used herein, the term "spin pack" refers to the entire assembly
for processing the molten polymer to produce extruded polymer
streams, including the polymer filtration, mixing and distribution
systems and the spinneret. As used herein, the term "spinneret"
refers to the portion of the spin pack which delivers the molten
polymer to and through orifices for extrusion into the environment.
The spinneret can be implemented with drilled holes through a plate
or any other structure capable of issuing the required fiber
streams.
An array of plural-component fibers 124 is formed from the polymer
streams exiting the spinneret 120 of spin pack 118 and is pulled
downward and attenuated by an aspirator 126 which is fed by
compressed air or steam from pipe 128. Aspirator 126 can be, for
example, of the gun type or of the slot type, extending across the
full width of the fiber array, i.e., in the direction corresponding
to the width of the web to be formed by the fibers. A typical
spinneret and aspirator arrangement useful for this process is
illustrated in U.S. Pat. No. 3,802,817, the disclosure of which is
incorporated herein by reference in its entirety.
Aspirator 126 delivers attenuated fibers 130 onto a web-forming
screen belt 132 which is supported and driven by rolls 134 and 136.
A suction box 138 is connected to a fan (not shown) to pull room
air (at the ambient temperature) through screen belt 132 and cause
fibers 130 to form a nonwoven web on screen 132.
Once the web is formed on screen 132, the web is treated to cause
the plural-component fibers to separate into their constituent
segments. For example, where the polymers of the fibers shrink to
different degrees upon application of heat, the web can be heated
to cause differential heat shrinkage of the two (or more) polymer
materials of the fibers. Specifically, when heated to a temperature
below their melting points, one of the polymers (e.g., polymer B)
shrinks, relative to its unheated size, more than the other polymer
(e.g., polymer A) shrinks relative to its unheated size. When the
difference in heat shrinkage is significant, crimping and
separation of the fiber segments occurs. A high degree of crimping
and splitting (separation) of the plural-component fibers is
desirable, since a lofty or bulky nonwoven fabric having good
softness, flexibility and drape characteristics and barrier
properties results. One particularly advantageous combination of
polymers is polypropylene (polymer A) and polyethylene terepthalate
(PET) modified with 20 mole percent purified isopthalic acid and a
powdered transesterification inhibitor (GE Ultranox 626) (polymer
B), which have a difference in heat shrinkage of approximately
thirty percent under the heating conditions of the present
invention.
Referring again to FIG. 16, to differentially heat shrink the
plural-component fibers, the web formed on web-forming belt 132
passes in close proximity to (e.g., directly under or over) a
heating unit 140 which causes the temperature of the fibers of the
web to increase to a temperature at which differential heat
shrinkage of polymers A and B occurs, thereby causing the
plural-component fibers to separate into their constituent
segments. That is, the temperature of the web is raised to a
temperature below the melting points of polymer A and polymer B but
high enough to sufficiently shrink at least one of the two polymers
to cause separation between adjacent segments of the fibers. As
used herein, the terms "separation" and "separate" connote
substantial detachment of segments from adjacent segments along at
least a substantial portion of the longitudinal extent of the
segments, but do not require total separation (although total
separation or nearly total separation is desirable and can be
achieved with certain polymer and process combinations).
Although substantial crimping of the fibers is not required by the
present invention, some crimping of the fibers may occur in
addition to fiber splitting to further increase the softness and
bulkiness of the fabric. For example, some degree of crimping of
the fiber segments typically occurs at the time of initial
shrinkage, the segments of the unseparated portions of the fibers
experience significant crimping due to the shrinkage difference
between the unseparated segments, and the segments of the separated
portions of the fibers may also experience some degree of crimping,
depending on the particular polymer components and the process
conditions.
Heating unit 140 can supply any type of heat suitable for causing
differential heat shrinkage and separation of the fiber components,
including, but not limited to: hot air blown through the web
(convection heating); steam blown through the web; radiant heat;
and combinations thereof. Heat can also be applied by subjecting
the web to hot or boiling water. Other techniques can be used
instead or in combination with heating to separate the
plural-component fibers, including, but not limited to, treatment
with chemicals, applying mechanical force to the fibers, such as
high pressure water jets, beating, carding, calendering, or other
mechanical working of the fibers. Alternatively, one of the
components of the plural-component fibers can be dissolved by a
solvent applied to the fiber, such that segments formed of the
undissolved component remain.
Referring once again to FIG. 16, after separation of the
plural-component fibers, the web passes through an optional
compaction roll 142 and then leaves the screen and passes through a
nip formed by heated calender rolls 144 and 146. One of the
calender rolls is embossed to have raised nodules which fuse the
fibers together only at the points where the nodules contact the
web, leaving the fibers between the bond points still bulky and
giving the resultant bonded nonwoven fabric good flexibility and
drape. Other conventional bonding techniques can be employed to
bond the web, including, but not limited to: through-air bonding
(particularly useful with the low melt temperature normally seen
with high shrinkage components); needle punching; and
hydroentangling (i.e., use of high-pressure water jets). In
particular, in accordance with the through-air bonding technique,
as heat is applied to the web, the temperature of the web rises to
a point at which differential shrinkage of the high-shrinkage
polymer component occurs. As heat continues to be applied, the
temperature of the web rises to a temperature to a point at which
the high-shrinkage polymer becomes tacky and begins to melt,
allowing the segments formed of high-shrinkage polymer to bond to
adjacent polymers.
While formation of a nonwoven fabric has been described in the
context of a spunbond process, the easily splittable
plural-component fibers of the present invention can be employed in
web or fabric forming processes that do not require bonding of the
fibers. For example, the differential heat shrinkage technique can
be applied in spunlaid processes.
Furthermore, the easily splittable plural-component fibers of the
present invention can be used to form woven fabrics. In this case,
the extruded and drawn plural-component fibers are wound on a
bobbin or other winding mechanism. Subsequently, the fibers are
used in a conventional knitting or weaving process to form a woven
fabric. The plural-component fibers can be split by employing one
of the aforementioned splitting techniques or by brushing or
sanding the fabric.
The process of forming fabric from the plural-component fibers of
the present invention is not limited to the particular apparatus
and processes described in connection with FIG. 16, and additional
or modified processing techniques are considered to be within the
scope of the invention. For example, one or more godets may be used
prior to the aspirator for drawing and/or relaxing the fibers. A
downstream godet may be operated at higher speed than an upstream
godet to stretch the fibers, or a downstream godet may be operated
at a lower speed than an upstream godet to relax the fibers.
While the above-described embodiments of forming a nonwoven fabric
rely principally on separation of the plural-component fibers of
the web after deposition of the plural-component fibers on the
web-forming surface, in accordance with the present invention,
measures may be taken to effect fiber splitting prior to deposition
of the fibers onto the web-forming surface. Techniques which result
in splitting or partial splitting of the fibers before laydown on
the web-forming belt may result in a fabric with better coverage
(free of open areas in the web) as well as the other advantageous
fabric qualities described herein, as the fiber segments are able
to lay down on the belt independently of each other. Specifically,
the aforementioned godet(s) may be heated to assist in differential
heat shrinkage of the fibers to facilitate splitting, and/or
another conductive heating device, such as a hot plate, can be
employed for this purpose.
Various splitting aids can also be employed, including, but not
limited to: fluoropolymer or silicone compounds in one or more of
the polymer components to make the components slippery and more
prone to split; foaming agents in one or more of the components
which induce swelling of one component relative to the other
component; and use of ultrasonics in addition to heat to excite the
two polymer components to enhance relative movement and
splitting.
The fine fiber segments separated by the system of the present
invention produce a desirably softer fabric with greater loftiness
and bulkiness than nonwoven fabrics made from known spunbond
processes. Various additional improved fabric properties, such as
good fabric drape, high filtration, barrier properties, and
coverage at low weight are also achieved with the ultra-low denier
per filament resulting from the split fibers of the present
invention.
Fabrics formed from the easily splittable plural-component fibers
produced by the process of the present invention are useful in any
product where properties such as softness, strength, filtration or
fluid barrier properties, and high coverage at a low fabric weight
are desirable or advantageous. For example, the fabric of the
present invention can be used in a variety of commercial products
including, but not limited to: softer diaper liners, sanitary
napkins, disposable wipes or other disposable absorbent articles;
medical fabrics having barrier properties such as surgical gowns
and drapes and sterilization wraps; filtration media and devices;
and liners for articles of clothing (e.g., a liner of a jacket).
The easily splittable plural-component fibers of the present
invention are also suitable in any product where a fluffy nonwoven
fabric is useful, such as thin sheets of padding.
The present invention is not limited to the particular apparatus
and processes described above, and additional or modified
processing techniques are considered to be within the scope of the
invention. For example, while described in the context of a
spunbond process, the easily splittable plural-component fibers of
the present invention can be use in web or fabric forming processes
that do not require bonding of the fibers. For example applied in
spun-laid or air carding processes. Further, the present invention
can be applied in melt blown systems.
Moreover, the benefits of using separated sub-fibers are not
limited to systems that form webs from continuous fibers. Thus, for
example, the present invention encompasses processes for forming
nonwoven fabrics from staple sub-fibers, wherein the fibers are cut
into short fibers prior to forming a web therefrom (either prior or
subsequent to fiber splitting). One potential advantage of
employing staple fibers is that, a more isotropic fabric can be
formed, since the staple fibers potentially can be oriented in the
web more randomly than continuous fibers.
In addition to nonwoven webs and fabrics composed solely of
separated sub-fibers from plural-component fibers, the
plural-component fibers of the present invention can be used in
combination with fibers of other transverse cross sections and in
combination with other technologies to form composite materials.
For example, other sheet technologies, such as melt blown or film
composites (including laminates) can be combined with the fiber
extrusion process of the present invention. The present invention
also encompasses mixed fiber embodiments, wherein separated
sub-fibers and conventional (e.g., non-split) fibers are
simultaneously spun from a single spinneret to produce a sheet of
mixed fiber composition. The fibers may be composed of a variety of
different resins. Finally, the present invention encompasses the
use of separated sub-fibers in thermobonded applications, whether
mixed, laminated or stratified.
Having described preferred embodiments of new and improved method
and apparatus for extruding easily-splittable plural-component
fibers for nonwoven fabrics, it is believed that other
modifications, variations and changes will be suggested to those
skilled in the art in view of the teachings set forth herein. It is
therefore to be understood that all such variations, modifications
and changes are believed to fall within the scope of the present
invention as defined by the appended claims.
* * * * *